Add another type JSPositiveInt to show a range analysis in the inferrer would be very beneficial :-…

sdk/lib/_internal/compiler/implementation/ssa/value_range_analyzer.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 
 class ValueRangeInfo {
   final ConstantSystem constantSystem;
 
@@ skipping 616 matching lines @@
         assert(range != null);
         ranges[instruction] = range;
       }
     }
 
     block.forEachPhi(visit);
     block.forEachInstruction(visit);
   }
 
   Range visitInstruction(HInstruction instruction) {
-    if (instruction.isUInt32(compiler)) {
+    if (instruction.isPositiveInteger(compiler)) {
       return info.newNormalizedRange(
           info.intZero, info.newPositiveValue(instruction));
     } else if (instruction.isInteger(compiler)) {
       InstructionValue value = info.newInstructionValue(instruction);
       return info.newNormalizedRange(value, value);
     } else {
       return info.newUnboundRange();
     }
   }
 
@@ skipping 169 matching lines @@
     if (left.isInteger(compiler)) {
       return tryComputeRange(left);
     } else if (right.isInteger(compiler)) {
       return tryComputeRange(right);
     }
     return info.newUnboundRange();
   }
 
   Range visitCheck(HCheck instruction) {
     if (ranges[instruction.checkedInput] == null) {
-      return info.newUnboundRange();
+      return visitInstruction(instruction);
     }
     return ranges[instruction.checkedInput];
   }
 
   HInstruction createRangeConversion(HInstruction cursor,
                                      HInstruction instruction) {
     JavaScriptBackend backend = compiler.backend;
     HRangeConversion newInstruction =
         new HRangeConversion(instruction, backend.intType);
     conversions.add(newInstruction);
@@ skipping 169 matching lines @@
   }
 
   Range handleBinaryOperation(HBinaryArithmetic instruction) {
     Range leftRange = visit(instruction.left);
     Range rightRange = visit(instruction.right);
     if (leftRange == null || rightRange == null) return null;
     BinaryOperation operation = instruction.operation(info.constantSystem);
     return operation.apply(leftRange, rightRange);
   }
 }